1. Field of the Invention
The present invention relates to an image forming apparatus configured to properly determine a discharge direction of a sheet, carrying a toner image fixed thereto by application of heat from a fixing unit, according to the type of the sheet.
2. Description of the Related Art
The Japanese Unexamined Patent Publication No. 2007-10696, for example, discloses a conventional image forming apparatus. The image forming apparatus of this Publication is so configured that a toner image is transferred from a peripheral surface of a photosensitive drum to a sheet in an image forming unit and the toner image is fixed to the sheet by application of heat in a fixing unit which includes a heating roller having a built-in heat source and a pressure roller disposed face to face with the heating roller. The toner image is fixed to the sheet as the sheet is passed through a nip formed between the heating roller and the pressure roller under conditions where the two rollers rotate in opposite directions.
In this image forming apparatus, a discharge condition of the sheet from the fixing unit can be properly set according to the type of the sheet. Specifically, the image forming apparatus is provided with a guide member located immediately downstream of the fixing unit. The guide member has a plurality of ribs along which an image carrying surface (i.e., a surface facing the heating roller) of the sheet discharged from the fixing unit is guided. These ribs include two types, that is, the first type ribs provided in a middle portion of the guide member with respect to a sheet width direction to guide thick, narrow-width sheets (such as post cards), and the second type ribs provided on both sides of the first type ribs to guide ordinary sheets. The image forming apparatus is further provided with a sheet deflection member disposed face to face with the first type ribs for forcing and deflecting the sheet discharged from the fixing unit in a direction toward the guide member.
The sheet deflection member is so structured as to be able to move toward and away from the first type ribs. When the sheet is a thick, narrow-width sheet, a driving member is actuated, causing the sheet deflection member to project toward the first type ribs, and when the sheet is an ordinary sheet, the driving member is actuated to move the first type ribs in a reverse direction, causing the sheet deflection member to return from a projected position to a home position.
When the thick, narrow-width sheet is discharged from the fixing unit, the sheet deflection member is caused to project so that the sheet is fed along the first type ribs which have been moved closer to the heating roller, thus lengthening a period of contact between the thick, narrow-width sheet which poorly absorbs toner and the heating roller. This arrangement makes it possible to carry out a fixing process in a reliable fashion and prevent a so-called toner offset phenomenon in which part of the toner image transfers to a peripheral surface of the heating roller due to incomplete execution of the fixing process.
When the thick sheet discharged from the fixing unit is pressed against the heating roller, the thick sheet which has softened as a result of application of heat bends toward the guide member. If the sheet is discharged onto a sheet delivery tray and cools in this condition, there arises a problem that the sheet assumes an inconveniently curled shape.